Molecular Dynamics Simulations of Reactions of Hyperthermal Fluorine Atoms with

Molecular dynamics simulations of the reactions between gaseous fluorine atoms and (SiFx)n adsorbates on the Si{100}-(2 × 1) surface are performed using the SW potential with the WWC reparameterization. The objective of the simulations is to determine how the chemical composition and energy distribution of the etched gas-phase products depend on the identity of the reacting adsorbate. Reactions of normal incident fluorine atoms with SiF3, SiF2-SiF3, and SiF2-SiF2-SiF3 adsorbates are simulated at incident kinetic energies from 3.0 to 9.0 eV. SiF4 is the major product in nearly all cases. An SN2-like mechanism is responsible for the formation of SiF4, Si2F6, and Si3F8. In addition, at 7.0 and 9.0 eV, the simulations have discovered a previously unknown mechanism for the formation of SiF4, which involves an insertion between a silicon-silicon bond. The simulations predict that radical species are formed predominantly from fragmentation of the higher mass etched products with only a few being formed directly from the reaction between the incoming fluorine atom and the adsorbate. Comparisons are made to experimental data on silicon-fluorine etching with both thermal and hyperthermal fluorine atoms. I